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The Secure realReal-time transport protocol Transport Protocol (Secure RTP or SRTP) is an IETF cryptographic protocol used to provide secure communications over an untrusted networkuntrusted networks as described in RFC 3711. SRTP provides confidentiality, message authentication and replay protection to Internet media traffic such as audio and video. The 

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supports Secure RTP and its associated secure real-time transport control protocol (Secure RTCP) for IPv4/IPv6 addressing for both audio and video streams.

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Secure RTP on the SBC is available using SIP signaling over UDP, TCP, and TLS (Transport Layer Security) protocol, and is signaled by specifying Secure RTP transport in an SDP (Session Description Protocol) media (m=) line. The

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uses the RFC4568 RFC 4568 Security Descriptions ("sdescriptions") standard for negotiating the use of Secure RTP. TLS over TCP is recommended for SIP transport when negotiating Secure RTP, because it protects the integrity and confidentiality of the sRTP keys which would otherwise be exposed. The 

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supports sRTP on all call legs.

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• Direct Media over SRTP/TLS between subscribers in the same Media Group for both audio and video calls.
• Direct Media between endpoints in the same media zone belonging to the same or different

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  . For example, Direct Media with TLS/SRTP is applicable for a distributed network containing two

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  s.

SRTP Crypto Suites

The

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 platforms support the following crypto suites for SRTP and SRTCP encryption:

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Caption 0 Table 1 SRTP and SRTCP Crypto Suites 3 SRTP and SRTCP Crypto Suites  Crypto Suite Master Key Length (bits) Salt Value (bits) Cipher Key Derivation Function Encryption key (bits) Message Authentication Code Authentication tag length (bits) Authentication key length (bits) AEAD-AES-128-GCM 128 96 AES-CM AES_CM PRF [RFC3711] 128 Galois Message Authentication Code (GMAC) 128 N/A AEAD-AES-256-GCM 256 96 AES-CM AES_256_CM_PRF [RFC6188] 256 Galois Message Authentication Code (GMAC) 128 N/A AES-CM-128-HMAC-SHA1-32 128 112 AES Counter Mode AES_128_CM_PRF 128 HMAC-SHA1 32 160 AES-CM-128-HMAC-SHA1-80 128 112 AES Counter Mode AES_128_CM_PRF 128 HMAC-SHA1 80 160 AES-CM-192-HMAC-SHA1-32 192 112 AES Segmented Integer Counter Mode AES_192_CM_PRF 192 HMAC_SHA1 32 160 AES-CM-192-HMAC-SHA1-80 192 112 AES Segmented Integer Counter Mode AES_192_CM_PRF 192 HMAC_SHA1 80 160 AES-CM-256-HMAC-SHA1-32 256 112 AES Segmented Integer Counter Mode AES_256_CM_PRF 256 HMAC_SHA1 32 160 AES-CM-256-HMAC-SHA1-80 256 112 AES Segmented Integer Counter Mode AES_256_CM_PRF 256 HMAC_SHA1 80 160

 

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